Although reference is primarily made hereafter to exhaust gas recirculating valves in motor vehicles, the present invention is not restricted thereto, but rather is directed to all types of friction-inhibited movement controls. The movements of robot arms, valve flaps in general, motors in general (e.g., electric, hydraulic, pneumatic), etc., are mentioned here solely as examples.
Exhaust gas recirculation control decreases the NOx emissions in partial-load operation. A continuously-variable EGR valve is used and its opening position is controlled for this exhaust gas recirculation from the exhaust pipe to the intake manifold. An EGR valve is typically driven by a DC motor, which is continuously activated by a control unit (e.g., ECU or EDC) via a so-called H bridge. A position feedback unit on the EGR valve provides a position actual value to the control unit. A PID position controller is typically used.
However, a PID position controller may only overcome the friction (static friction and/or sliding friction) with the I (integral) component. The amplification of the I component must be kept small, however, to prevent oscillation of the control circuit at low frequencies. Therefore, it accordingly takes a long time until, e.g., the static friction is overcome. Slow, triangular pumping of the I component results, at an amplitude which corresponds to the static friction.
It is therefore desirable to provide an improved control for friction-inhibited movements.